Just got my Speed Pro molly rings yesterday(Not file fit). I was expecting to find on the instruction sheet the recommeded end gap to be used with their Hypereuectic pistons. However no gap recommendations were specified for any pistons. I see in the book How to build Max Performance in a BB that the recommended street gap on should be .016 -.018. Again this does not specify forged, cast or hyper. Are these #'s what I should go by?

 

contact them!!!!!! :thumbs:

 

Why would ring gap change with pistons?? The rings are free floating in the groove and against the bore. Regardless of what the pistons are the gap doesn't change. The application changes the gap like blown or supercharged but not the pistons.
I personally would leave them alone. Check a few with the proper technic but don't file fit them unless they are required as file fit.

 

Ring end gap does not vay by piston type. The ring manufacturer will specify ring gap for their ring type. Tyipcally, moly rings should be run at .0045" gap per inch of bore for the top ring and .0055" gap per inch of bore on the second ring. This will usually put you in the .016" - .018" gap range for the top ring on a small block. High performance, supercharged and nitrous-sprayed engines need a little more gap.

 

Thanks for the info. I thought that I had read or heard some where that hypereuectic pistons can or should run closer end gaps because they do not expand as much. The rings that I bought are not file fit they are just regular .030 454 molly rings. I planned on checking them and hoped that no filing would be needed. Just trying to make sure that my facts are straight. The info provided in the Max Performance for BB book I referred to was taken from Speed Pro which is what I have for pistons and rings.

thanks
Wade

 

Hypereutectic pistons can be run with tighter cylinder wall clearances due to more cotrolled expansion. This does not affect the ring gap, since the rings expand independently of the pistons.

 

Thanks for the info Lars. I just got finished checking each individual 1st ring in each cylinder. All fail right in the .016-.018 range.

thanks
Wade :seeya


[Modified by BlackRat, 6:04 PM 1/22/2004]

 

I hate to swim against the tide here, but hypereutectic pistons will generally require a larger top ring gap than their "normal" cast or forged cousins. The top rings run hotter and, therefore, require a wider gap to prevent butting and catastrophic failure of the unit.

Here's a link to the story in a nutshell. http://www.jjsales.com/requirements.htm

The old Keith Black site used to have a very long treatise on hyperslugs and a similar chart showing the special top ring gap factors required for hypereutectics.

The reason I did this research a while back is because I got bit by a "too-tight" (standard) ring gap on some hypers I had installed in my old 415. The short version is that the top ring gap closed and the ends butted. This locked the top of the piston at the top of the cylinder. The rest of the piston, however, kept bopping up and down until it shattered like glass and allowed the rod and wristpin to poke a hole in the block.

Made lots of nice smoke and steam, though.

I would seriously consider setting the top ring gaps somewhere in the .020"-.024" range--depending on your cylinder bore diameter--if I were you. But, hey. What do I know?



[Modified by The Dude, 4:34 PM 1/22/2004]

 

Good catch.

 

yes, good catch :cheers:
i'm surprised lars and norval missed it.
.020-.024 sounds good, more needed with nitrous or high A/F ratios.
i still give norval and lars a 99 which is hard to beat :D

 

i agree with the dude,ive run keith black hyper. pistons in a half dozen motors and they require larger top ring gaps,ive seen a few motors of other guys not doing it and they have taken the top ring land right off from the ring butting.But some hyper. piston manufactures say you dont have to do it with theres,such as speed pro and others.just check with maufacturer.

"Top ring gaps can be increased 50% with hypereutectic pistons"


[Modified by patsnitrovette, 8:54 PM 1/22/2004]


[Modified by patsnitrovette, 9:00 PM 1/22/2004]

 

keith black reccomended .030 for the top ring because the material used in the piston holds the heat more that std aluminum pistons causing the top ring to grown more than with std pistons. :chevy


[Modified by clem zahrobsky, 8:58 PM 1/22/2004]

 

I agree with Pat. I've seen this several times with hypereuectic pistons. Breaks the top right off and breaks the ring. Looks almost the same as running too lean, too long. The piston manufacturer is the best source for gap info.

 

Curiuos as why the piston manufacturer would be the one to talk, seems you would want to talk to the ring manufacturer, it is the ring not the piston that is the variable. Knowing what type and brand of pistons might play a role in detrmining what gap to run. Of course the piston manufacturer might already know what gap to run with a particular kind and brand of ring but i would still consult the ring manufacturer to be safe.

You don't call a rim manufaturer to find out what poundage to run a tire at do ya? :)

 

You have to reference both the ring manufacturer and the piston manufacturer. Years of experience in the field (or a personal major catastrophe) are the only things that help you make a decision when there is conflicting information. I run into this all of the time.

I have contacted suppliers and gotten the "whateva" attitude on many occasions. That doesn't cut it. You have to do your homework and follow through on the details if you're going to assemble an engine.

Close only counts in horse-shoes & grenades.

 

I just did this, using KB hyper pistons and thier instructions were quite clear that the top ring end gap had to be larger. I don't emember exactly what it is at the moment but check with the piston manufacturer for thier recommendations

 

Just got off the phone with the federal Mogul tech line. (1-800-325-8886) Since I am running there pistons and rings the street performance gap is between .016-.018. They told me that they do not require a wider ring gap on there hyper pistons becuase the top ring bed is not as close to the top of the oiston as the KB's. He specifically sited the KB piston as requiring the larger gap because of the closeness of the top ring to the combustion chamber which creates greater heat around the top ring and has resulted in the failures you guys have mentioned when the correct end gap was not used. I explained to them how my engine was setup and what it was to be used for and he said that I needed to go with the .016-.018 gap and I would be fine.

Thanks for all the input guys. Hopefully this thread will be usefull to others.

Wade :thumbs:

 

Just an FYI.

While I got the top ring gap information from Keith Black after my other engine blew up, you really ought to know that the affected piston was a Federal-Mogul piece--an H615P to be precise.

I'd talk with your ring manufacturer. Assuming you have a standard-bore 454 your top ring gap ought to be: 4.250 x .0065 = .027" -.028".

I'd just really hate to see you go through all the time and effort and spend all the money just to possibly have to do it over in a few weeks or months. If that engine lets go the way mine did you'll only be able to salvage the intake, plug wires, distributor and MAYBE the timing cover and oil pan.

Take this for what it's worth. Good luck.



[Modified by The Dude, 9:14 AM 1/23/2004]

 

Dude,

thanks for the info. My rings are also Speed Pro rings. So this puts me in a little bit of a dilema as to what to do. The manufacturer says that I am fine with the gaps at .016-.018. But some experiences are saying otherwise. :confused: :banghead:

Wade